INTRAFORMATIONAL CORRUGATED ROCKS 589 



The explanation offered by the writer is that the contorted 

 zones were produced by differential movements within the mass of 

 the Trenton limestone. The displacement (140 feet) of the thrust 

 fault at Prospect Village was sufficient to cause the beds of the 

 middle Trenton to be shoved over the upper Trenton. Figure i 

 (lower part) shows the relation of the contorted zones to this fault. 

 It is easy to see how, when the force of compression was brought to 

 bear in this region, the higher Trenton beds on the upthrow side 

 must have moved more easily and consequently faster than the 

 lower Trenton beds. For instance, the portion A in Figure i 

 (lower part) being separated from C by an intermediate mass B 

 of possibly slightly less rigidity moved over C and caused the 

 portion B to become ruffled or folded and fractured because this 

 portion took up most of the differential movement. The portion B 

 needed to be only slightly less rigid than the adjacent strata and 

 this slightly reduced competency is due to somewhat thinner 

 limestone layers separated by relatively thicker shale partings. 

 A similar explanation applies to the lower contorted zone. Accord- 

 ing to this explanation the corrugated zones indicate horizons along 

 which the differential movements took place, and no great amounts 

 of differential movement were necessary to produce the contortions. 



Grabau^ states that 



These disturbances at Trenton Falls have been variously explained, the 

 general conclusions of geologists being either: (i) that they were truly tectonic 

 — lateral pressure having resulted in the folding of certain strata while others 

 took up the thrust without deformation, or (2) that they were due to squeezing 

 out of certain layers under the weight of overlying rock masses. Both explana- 

 tions are unsupported by the detailed characteristics of the folds and their 

 relationship to the enclosing layers. 



The writer agrees that these two explanations must be ruled out, 

 but he does not agree with Grabau who accepts Hahn's^ subaqueous 

 slumping or gliding hypothesis, described later in this paper, without 

 even mentioning the tectonic differential slipping hypothesis (above 

 outlined) which was first applied by the writer^ to the Trenton 



'A. W. Grabau, Principles of Stratigraphy (1913), p. 784. 



^ F. Hahn, Neues Jahrb. BeiL, Vol. XXXVI (1913), pp. 1-40. 



3 W. J. Miller, Jour. GeoL, Vol. XVI (1908), pp. 428-33. 



